Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C16/00—Erasable programmable read-only memories
  • G11C16/02—Erasable programmable read-only memories electrically programmable
  • G11C16/06—Auxiliary circuits, e.g. for writing into memory
  • G11C16/24—Bit-line control circuits
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C16/00—Erasable programmable read-only memories
  • G11C16/02—Erasable programmable read-only memories electrically programmable
  • G11C16/06—Auxiliary circuits, e.g. for writing into memory
  • G11C16/26—Sensing or reading circuits; Data output circuits
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C16/00—Erasable programmable read-only memories
  • G11C16/02—Erasable programmable read-only memories electrically programmable
  • G11C16/06—Auxiliary circuits, e.g. for writing into memory
  • G11C16/26—Sensing or reading circuits; Data output circuits
  • G11C16/28—Sensing or reading circuits; Data output circuits using differential sensing or reference cells, e.g. dummy cells
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C16/00—Erasable programmable read-only memories
  • G11C16/02—Erasable programmable read-only memories electrically programmable
  • G11C16/06—Auxiliary circuits, e.g. for writing into memory
  • G11C16/32—Timing circuits
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C7/00—Arrangements for writing information into, or reading information out from, a digital store
  • G11C7/06—Sense amplifiers; Associated circuits, e.g. timing or triggering circuits
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C16/00—Erasable programmable read-only memories
  • G11C16/02—Erasable programmable read-only memories electrically programmable
  • G11C16/04—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS
  • G11C16/0408—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors
  • G11C16/0425—Erasable programmable read-only memories electrically programmable using variable threshold transistors, e.g. FAMOS comprising cells containing floating gate transistors comprising cells containing a merged floating gate and select transistor

Definitions

• Flash memory systems are well-known. In typical flash memory systems, a sense amplifier is used to read data from a flash memory cell.
• Figure 1 depicts a prior art sense amplifier 100.
• Sense amplifier 100 comprises selected flash memory cell 102, which is the cell to be read.
• Sense amplifier 100 also comprises reference flash memory cell 122, against which selected flash memory cell 102 is compared.
• PMOS transistors 104, 106, 124, and 126 and NMOS transistors 108, 110, 112, 128, and 130 are arranged as shown.
• PMOS transistor 104 is controlled by CASREF (column address sensing reference)
• PMOS 106 is controlled by SEN_B (sense amplifier enable, active low)
• NMOS transistors 108, 112, and 128 are controlled by ATD (address transition detection, which detects a change in the received address)
• NMOS transistors 110 and 130 are controlled by YMUX (Y multiplexor) which activates a BL (bit line).
• Selected flash memory cell 102 receives WL (word line) and SL (source line)
• reference memory cell 122 receives SL (source line).
• Comparator 130 receives two inputs that are directly related to the current drawn by selected flash memory cell 102 and reference memory cell 122, and the output SOUT is directly indicative of the data value stored in selected flash memory cell 102.
• One drawback of prior art sense amplifier 100 is that a constant current is drawn by memory cell 102 and its associated circuitry, which results in significant power consumption.
• reference memory cell 122 and its associated circuitry typically are provided in a separate read bank than the read bank in which selected memory cell 102 is located, which requires a large die area and more power consumption for additional Y-decoding.
• the CASREF signal also is sensitive to noise, and the CASREF circuit also consumes significant standby current.
• Figures 2, 3A, and 3B depict improved sense amplifier 200 previously designed by Applicant, and which is described in China Patent Application 201511030454.4, filed on December 31, 2015, and titled“Fow Power Sense Amplifier for a Flash Memory System,” which is incorporated herein by reference.
• sense amplifier 200 comprises reference circuit 280 and read circuit 290.
• Reference circuit 280 comprises reference memory cell 206, NMOS transistors 202, 204, and 220, PMOS transistor 212, reference bit line 208, level shifter 214, inverter 218, and NOR gate 216, all configured as shown.
• NMOS transistor 202 is controlled by ATD (address transition detection)
• NMOS transistor 204 is controlled by YMUX (Y multiplexor)
• NMOS transistor 220 is controlled by a BIAS signal.
• NOR gate 216 receives ATD as one of its inputs.
• Read circuit 290 comprises selected memory cell 236, NMOS transistors 232, 234, and 250, PMOS transistor 242, bit line 238, , level shifter 244, inverter 248, and NOR gate 246, all configured as shown.
• NMOS transistor 232 is controlled by ATD (address transition detection)
• NMOS transistor 234 is controlled by YMUX (Y multiplexor)
• NMOS transistor 250 is controlled by a BIAS signal.
• NOR gate 246 receives ATD as one of its inputs.
• reference circuit 280 and read circuit 290 are identical, except that reference circuit 280 comprises reference memory cell 206, and read circuit 290 comprises selected memory cell 236.
• sense amplifier 200 works as follows. Prior to a read operation, the BIAS signal is high, which pulls the voltage at the output of inverters 218 and 248 to ground through NMOS transistors 220 and 250, which causes ROUT and SOUT to be high. At the beginning of a read operation, ATD goes high, which signifies a detection in the change of the address received by the memory system, which coincides with the beginning of a read operation.
• NMOS transistors 202 and 232 are turned on, as are NMOS transistors 204 and 234 by YMUX. This allows reference cell 206 and selected memory cell 236 to draw current. Concurrently, reference bit line 208 and bit line 238 will begin charging.
• BIAS also goes low at the beginning of the read operation. At this stage, PMOS transistors 212 and 242 are off, as the voltage on its gate will be high.
• ATD will then go low, which shuts off NMOS transistors 202 and 232.
• Reference bit line 208 will begin discharging through reference cell 206. As it does so, the voltage of reference bit line 208 will decrease, and at some point will drop low enough (below VREF) such that PMOS transistor 212 turns on. This causes ROUT to drop to low.
• bit line 238 also is discharging through selected memory cell 236. As it does so, the voltage of bit line 238 will decrease, and at some point will drop low enough (below VREF) such that PMOS transistor 242 turns on. This causes SOUT to drop to low.
• each sense amplifier has a local feedback (216, 218 or 246, 248) to cut off its bias current, which reduces the power consumption. [0012] Essentially, there is a race condition between reference circuit 280 and read circuit 290.
• SOUT and ROUT are input into timing comparison circuit 260, and the output is DOUT, which indicates the value stored in selected memory cell 236.
• FIG. 3A depicts a first embodiment of timing comparison circuit 260.
• timing comparison circuit 260 comprises flip-flop 310, with SOUT as the D input, ROUT as the active low clock CK, and DOUT as the output.
• SOUT goes low before SOUT
• DOUT will output a "0,” indicating that selected memory cell 236 is storing a "0.”
• ROUT goes low after SOUT
• DOUT will output a "1," indicating that selected memory cell 236 is storing a "1.”
• FIG. 3B depicts a second embodiment of timing comparison circuit 260, which comprises an R-S latch.
• Timing comparison circuit 260 comprises inverters 320 and 322 and NAND gates 324 and 326 configured as shown, with SOUT and ROUT as inputs, and DOUT as the output.
• An improved low-power sense amplifier for use in a flash memory system is disclosed.
• the reference bit line and selected bit line are pre-charged during a limited period and with limited power consumed.
• the pre-charge circuit can be trimmed during a configuration process to further optimize power consumption during the pre-charge operation.
• Figure 1 depicts a prior art sense amplifier in a flash memory system.
• Figure 2 depicts an embodiment of a low-power sense amplifier for a flash memory system previously disclosed by Applicant.
• Figure 3A depicts an embodiment of a timing circuit for use in a sense amplifier.
• Figure 3B depicts another embodiment of a timing circuit for use in a sense amplifier.
• Figure 4 depicts another embodiment of the low-power sense amplifier for a flash memory system.
• Figure 5 depicts a trimming operation of the sense amplifier of Figure 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Figure 4 depicts sense amplifier 400.
• Sense amplifier 400 comprises reference circuit 410 and read circuit 430.
• Reference circuit 410 comprises reference memory cell 411, NMOS transistors 412, 416, and 419. PMOS transistor 418, switch 414, node 415, reference bit line 417, inverter 420, and variable capacitor 413, all configured as shown.
• NMOS transistor 412 is controlled by VB
• NMOS transistor 416 is controlled by YMUX (part of a column decoder for selecting the column containing reference memory cell 411)
• NMOS transistor 419 is controlled by BIAS
• switch 414 is controlled by ATD (address transition detection)
• PMOS transistor 418 is controlled by node 415.
• Read circuit 430 comprises selected memory cell 431, NMOS transistors 432, 436, and 439.
• NMOS transistor 432 is controlled by VB
• NMOS transistor 436 is controlled by YMUX (part of a column decoder for selecting the column containing selected memory cell 431)
• NMOS transistor 439 is controlled by BIAS
• switch 434 is controlled by ATD (address transition detection)
• PMOS transistor 438 is controlled by node 435.
• sense amplifier 400 works as follows. Prior to a read operation, the BIAS signal is high, which turns on NMOS transistors 419 and 439 and pulls the input of inverters 420 and 440 to ground, which causes ROUT and SOUT to be high. At the beginning of a read operation, ATD goes high, which signifies a detection in the change of the address received by the memory system, which coincides with the beginning of a read operation. When ATD goes high, switches 414 and 434 are closed. NMOS transistors 416 and 436 are turned on by YMUX. This allows reference cell 411 and selected memory cell 431 to draw current.
• variable capacitors 413 and 433 will be storing a voltage that was generated during a charging process by voltage NMOS transistors 412 and 432 before switches 414 and 434 were closed. After switches 414 and 434 are closed, the charges on capacitors 413 and 433 are shared to nodes 415 and 435, respectively, in a short period. Meanwhile, reference cell 411 will draw current from variable capacitor 413, and selected cell 431 will draw current from variable capacitor 433.
• ATD will then go low, which opens switches 414 and 434.
• Node 415 and reference bit line 417 will continue discharging through reference cell 411.
• the voltage of node 415 will decrease, and at some point will drop low enough (below VDDS-Vthp, where VDDS is a voltage source provided to PMOS transistors 418 and 438 and Vthp is the threshold voltage of PMOS transistors 418 and 438) such that PMOS transistor 418 turns on.
• VDDS-Vthp the threshold voltage of PMOS transistors 418 and 43
• Timing comparison circuit 260 can comprise the structures described previously with respect to Figures 3A or 3B or can comprise another timing circuit.
• Figure 5 depicts a configuration phase for reference circuit 410 and read circuit 430.
• Trim controller 510 optionally can adjust the voltage VDDS using known techniques. Similarly, trim controller 510 can adjust the capacitance of variable capacitors 413 and 433 to alter the voltage that is initially provided to nodes 415 and 435 when ATD goes high and switches 414 and 434 are closed.
• references to the present invention herein are not intended to limit the scope of any claim or claim term, but instead merely make reference to one or more features that may be covered by one or more of the claims.
• Materials, processes and numerical examples described above are exemplary only, and should not be deemed to limit the claims.
• the terms“over” and“on” both inclusively include“directly on” (no intermediate materials, elements or space disposed there between) and“indirectly on” (intermediate materials, elements or space disposed there between).
• the term“adjacent” includes“directly adjacent” (no intermediate materials, elements or space disposed there between) and“indirectly adjacent” (intermediate materials, elements or space disposed there between).
• forming an element“over a substrate” can include forming the element directly on the substrate with no intermediate materials/elements there between, as well as forming the element indirectly on the substrate with one or more intermediate materials/elements there between.

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• 2018
  • 2018-06-15 CN CN201810619270.9A patent/CN110610738B/zh active Active
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• 2019
  • 2019-05-04 JP JP2020569844A patent/JP7244550B2/ja active Active
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